The invention concerns a fluid-flow meter for measuring a fluid under pressure. The flow meter includes a pressure-resistant outer housing in which a measuring-chamber housing with a movable measuring part is arranged, and a fluid medium in the space between the outer housing and the measuring-chamber housing which is at a pressure corresponding to the pressure of the fluid to be measured.
Fluid-flow meters for measuring fluids under pressure must be constructed so that their components which are important for measurement, particularly the measuring chamber machined to close tolerances, are not deformed, or only negligibly so, under the high pressure of the fluid, as otherwise, the functioning or at least the measuring accuracy would be adversely affected.
To meet these requirements in the commercially available flow meters described above, the space between the outer housing and the measuring-chamber housing is also filled with the liquid under pressure, which is to be measured. In this way, in these commercially available flow meters, the pressure outside and inside the measuring-chamber housing is practically equal. The measuring-chamber housing which, because of the required corrosion resistance, must frequently be made of high-quality material, can then be made with thin walls, which has a favorable effect on the manufacturing costs.
A flow meter constructed in this manner, however, has the important disadvantage that also the outer housing must be made of high-quality material because, if the fluids to be measured are corrosive, it must also be resistant to corrosion. Because the outer housing must be able to withstand the pressure of the fluid to be measured, it must be made correspondingly stable and this requires a relatively large amount of high-cost material. The manufacturing costs are therefore unfavorably high for this known flow meter. It is another important disadvantage of the known flow meter that it cannot be used very well in the food industry because it can hardly be cleaned, or only with great difficulty.